La microflore de diatomées du Messinien de Gibellina (Sicile occidentale, Italie)

In the western part of Sicily, only a few outcrops in the sector of Gibellina, southeast of the city of Salemi, allow the observation of Messinian bearing-diatom sediments, just under the massive gypsum formation. Here we observe diatomitic laminites within a marly-carbonate series containing gypsum levels. Among these laminites, towards the visible base of the series, are levels rich in very big diatom frustules and, higher in the succession, bitumineous laminites. The majority of the analyzed samples consists essentially of planktonic diatoms, except one level where benthic pennate diatoms dominate. The diatom assemblages characterize a marine opened environment, but are subject to littoral influences and sometimes even to freshwater contributions. The succession of the dominant diatom assemblages suggests an alternation between stratified water periods and blooms periods linked to possible upwellings.